Ionic & Covalent BondingElectronegativity & Polarity

Atoms react because

atoms must have a full outer energy level in order to be stable.

8 electrons

Atoms will gain, lose, or share electrons.

How atoms react depends on their electron configuration.

This atom will lose one electron.

This atom will gain one electron.

The type of bonding that results from the transfer of electrons is called _____________ionic bonding.

How atoms react depends on their electron configuration.

This atom will share four electrons.

The type of bonding that results from the sharing of electrons is called _________________covalent bonding.

How atoms react depends on their ability to attract electrons.

This atom only needs one electron so it has a very high affinity for electrons, it has a large electronegativity.

This atom wants to lose this electron it has very little affinity for electrons, it has very low electronegativity.

Electronegativity is the relative tendency of an atom to attract electrons to itself.

ELECTRONEGATIVITIES of the ELEMENTS

Fluorine is the most electronegative.

H2.1

ELECTRONEGATIVITIES of the ELEMENTS

Nonmetals have the highest electronegativities.

ELECTRONEGATIVITIES of the ELEMENTS

Metals have the lowest electronegativities.

Which are the most reactive metals? What do metals do?

The most reactive metals have lowest electronegativity.

Metals give away electrons.

Earlier we learned….

Ionic compounds form between a metal and a nonmetal.

Molecular compounds form betweena nonmetal and a nonmetal.

Why is this so…..ELECTRONEGATIVITY

The type of bonding (ionic or covalent) that occurs between atoms of two elements can be determined by calculating the difference in the element’s electronegativities .

Large difference in electroneg = Ionic bond

metal

nonmetal

Small difference in electroneg = Covalent bond

nonmetal

nonmetal

Ionic bond or covalent bond?

NaCl The electronegativity difference between sodium and chlorine is:

Na = 0.9 Cl = 3.0 3.0 – 0.9 = 2.1

A electronegativity difference of 1.7 or greater indicates an ionic bond.

Ionic bond

Ionic compound

HCl The electronegativity difference between hydrogen and chlorine is:

H = 2.1 Cl = 3.0 3.0 – 2.1 = 0.9

A electronegativity difference of less than 1.7 indicates a covalent bond.

Covalent bond

Molecular compound

Ionic bond or covalent bond?

MgO The electronegativity difference between magnesium and oxygen is:

Mg = 1.2 O = 3.5 3.5 – 1.2 = 2.3

A electronegativity difference of 1.7 or greater indicates an ionic bond.

Ionic bond

Ionic compound

Ionic bond or covalent bond?

H2O The electronegativity difference between hydrogen and oxygen is:

H = 2.1 O = 3.5 3.5 – 2.1 = 1.4

A electronegativity difference of less than 1.7 indicates a covalent bond.

Covalent bond

Molecular compound

Ionic bond or covalent bond?

Covalent bond < 1.7

Ionic bond or covalent bond?

Ionic bond > 1.7

Polarity is the property of having poles, a positive end and a negative end.

YES!!!Are ionic compounds polar?

BOND POLARITY

The greater the difference in electronegativity between two atoms, the more polar their bond.

Most covalent bonds have some ionic characteristic, that is, they are somewhat polar.

Covalent bonds involve electrons sharing between two atoms.

The bonding pairs of electrons in covalent bonds are pulled between the two nuclei.

When identical atoms are bonded together, the two atoms pull equally and the bonding electrons are shared equally ... nonpolar covalent bond.

Nonpolar covalent bonds exist when the two atoms bonded are identical.

3.0 - 3.0 = 0

A polar covalent bond is a covalent bond between atoms in which the electrons are not shared equally.

δ+δ+

δ-

Oxygen is more electronegative than hydrogen therefore oxygen pulls the bonding electrons toward itself thereby acquiring a partial negative charge.

The hydrogen is left with a partial positive charge.

O 3.5 H 2.1

The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less electronegative atom acquires a slightly positive charge.

δ+δ+

δ-

H ClCl 3.0H 2.1

δ-δ+

H ClThe polarity of the bond can be represented by an arrow pointing to the more electronegative atom and a crossed tail situated at the positive pole.

The arrow represents a dipole. A dipole is a molecule having two poles.

HCl is a polar molecule, it has a negative pole and a positive pole.

Water has two dipoles.

δ+ δ+

δ- δ-

Each bond in water is polar.

The effect of polar bonds on the polarity of an entire molecule depends on the shape of the molecule and the orientation of the polar bonds.

δ+ δ+

δ-

The water molecule is polar.

Is carbon dioxide a polar molecule?

C = 2.5 O = 3.5

The effect of polar bonds on the polarity of an entire molecule depends on the shape of the molecule and the orientation of the polar bonds.

The carbon dioxide molecule has two dipoles and is linear.Because the dipoles are the same magnitude but in opposite directions, they cancel each other out.

As a result, the molecule is nonpolar.

N = 3.0 H = 2.1

Is ammonia, NH3 a polar molecule?

YES

Is CCl4 a polar molecule?

C = 2.5 Cl = 3.0

The dipoles cancel so the molecule is not polar.